Gallium nitride and related III-V nitride materials such as GaN, InGaN, AlGaN and AlGaInN have a direct band gap that is continuously adjustable between 0.7-6.2 eV. They are suitable for use in a variety of devices, such as optoelectronic and microelectronic devices that operate in a wide spectral range from ultraviolet to infrared. Nevertheless, dislocations in III-V nitride materials may cause electrical defects that may limit the lifetime of the devices.
FIG. 1 illustrates a GaN-based device 100. The GaN-based device is generally formed by growing an epitaxial layer on a substrate. As illustrated in FIG. 1, the device 100 comprises a sapphire substrate 102, an N-type GaN layer 104 deposited on the sapphire substrate 102, an active layer 106 deposited on the N-type GaN layer 104, and a P-type GaN layer 108 deposited on the active layer 106. An N-type electrode 110 is deposed on the N-type GaN layer 104, and a P-type electrode 112 is deposed on the P-type GaN layer 108. The device 100 is electrically connected to an external power source through the N electrode 110 and the P electrode 112. During operation, a current passes from the P-type electrode 112 into the N-type electrode 108 via the P-type GaN layer 110, the light emitting layer 106, and the N-type GaN layer 104.
Currently, most GaN-based devices have been manufactured by heteroepitaxial deposition of GaN-based layers on the substrates. During the deposition of the GaN-based layers, heteroepitaxy is performed on highly lattice and mismatched substrates such as sapphire or silicon which invariably induces a high density of dislocations. The resulting heteroepitaxial layers are therefore highly defected and highly conducting as a result of defects and impurities.